CHAPTER 4 THREE MAJOR CLASSES OF CHEMICAL REACTIONS

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1 CHAPTER 4 THREE MAJOR CLASSES OF CHEMICAL REACTIONS END OF CHAPTER PROBLEMS 4.1 Plan: Review the discussion on the polar nature of water. Water is polar because the distribution of its bonding electrons is unequal, resulting in polar bonds, and the shape of the molecule (bent) is unsymmetrical. 4.2 Plan: Solutions that conduct an electric current contain electrolytes. Ions must be present in an aqueous solution for it to conduct an electric current. Ions come from ionic compounds or from other electrolytes such as acids and bases. 4. Plan: Review the discussion on ionic compounds in water. The ions on the surface of the solid attract the water molecules (cations attract the negative ends and anions attract the positive ends of the water molecules). The interaction of the solvent with the ions overcomes the attraction of the oppositely charged ions for one another, and they are released into the solution. 4.4 Plan: Recall that ionic compounds dissociate into their ions when dissolved in water. Examine the charges of the ions in each scene and the ratio of cations to anions. a) CaCl2 dissociates to produce one Ca 2 ion for every two Cl ions. Scene B contains four 2 ions and twice that number of 1 ions. b) Li 2 SO 4 dissociates to produce two Li 2 ions for every one SO 4 ion. Scene C contains eight 1 ions and half as many 2 ions. c) NH 4 Br dissociates to produce one NH 4 ion for every one Br ion. Scene A contains equal numbers of 1 and 1 ions. 4.5 Plan: Write the formula for magnesium nitrate and note the ratio of magnesium ions to nitrate ions. Upon dissolving the salt in water, magnesium nitrate, Mg(NO) 2, would dissociate to form one Mg 2 ion for every two NO ions, thus forming twice as many nitrate ions. Scene B best represents a volume of magnesium nitrate solution. Only Scene B has twice as many nitrate ions (red circles) as magnesium ions (blue circles). 4.6 Plan: Review the discussion of ionic compounds in water. In some ionic compounds, the force of the attraction between the ions is so strong that it cannot be overcome by the interaction of the ions with the water molecules. These compounds will be insoluble in water. 4.7 Plan: Review the discussion of covalent compounds in water. Some covalent compounds that contain the hydrogen atom dissociate into ions when dissolved in water. These compounds form acidic solutions in water; three examples are HCl, HNO, and HBr. 4.8 Plan: Compounds that are soluble in water tend to be ionic compounds or covalent compounds that have polar bonds. Many ionic compounds are soluble in water because the attractive force between the oppositely charged ions in an ionic compound are replaced with an attractive force between the polar water molecule and the ions when the compound is dissolved in water. Covalent compounds with polar bonds are often soluble in water since the polar bonds of the covalent compound interact with those in water. 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-1

2 a) Benzene, a covalent compound, is likely to be insoluble in water because it is nonpolar and water is polar. b) Sodium hydroxide (NaOH) is an ionic compound and is therefore likely to be soluble in water. c) Ethanol (CH CH 2 OH) will likely be soluble in water because it contains a polar OH bond like water. d) Potassium acetate (KC2H O 2 ) is an ionic compound and will likely be soluble in water. 4.9 Plan: Compounds that are soluble in water tend to be ionic compounds or covalent compounds that have polar bonds. Many ionic compounds are soluble in water because the attractive force between the oppositely charged ions in an ionic compound are replaced with an attractive force between the polar water molecule and the ions when the compound is dissolved in water. Covalent compounds with polar bonds are often soluble in water since the polar bonds of the covalent compound interact with those in water. a) Lithium nitrate is an ionic compound and is expected to be soluble in water. b) Glycine (H 2 NCH 2 COOH) is a covalent compound, but it contains polar N H and O H bonds. This would make the molecule interact well with polar water molecules, and make it likely that it would be soluble. c) Pentane (C5H 12 ) has no bonds of significant polarity, so it would be expected to be insoluble in the polar solvent water. d) Ethylene glycol (HOCH2CH 2 OH) molecules contain polar O H bonds, similar to water, so it would be expected to be soluble Plan: Substances whose aqueous solutions conduct an electric current are electrolytes such as ionic compounds, acids, and bases. a) Cesium bromide, CsBr, is a soluble ionic compound, and a solution of this salt in water contains Cs and Br ions. Its solution conducts an electric current. b) HI is a strong acid that dissociates completely in water. Its aqueous solution contains H and I ions, so it conducts an electric current Plan: Substances whose aqueous solutions conduct an electric current are electrolytes such as ionic compounds, acids, and bases. a) Potassium sulfate, K2SO 4, is an ionic compound that is soluble in water, producing K 2 and SO 4 ions. Its solution conducts an electric current. b) Sucrose is neither an ionic compound, an acid, nor a base, so it would be a nonelectrolyte (even though it s soluble in water). Its solution does not conduct an electric current Plan: To determine the total moles of ions released, write an equation that shows the compound dissociating into ions with the correct molar ratios. Convert mass and formula units to moles of compound and use the molar ratio to convert moles of compound to moles of ions. a) Each mole of KPO 4 forms moles of K ions and 1 mole of PO 4 ions, or a total of 4 moles of ions: KPO 4 (s) K (aq) PO 4 (aq) 4 mol ions Moles of ions = ( 0.75 mol KPO4) =.0 mol of ions. 1 mol KPO4 b) Each mole of NiBr 2 H 2 O forms 1mole of Ni 2 ions and 2 moles of Br ions, or a total of moles of ions: NiBr 2 H 2 O(s) Ni 2 (aq) 2Br (aq). The waters of hydration become part of the larger bulk of water. Convert mass to moles using the molar mass. 1 mol NiBr 2 H 2O mol ions Moles of ions = ( 6.88 x 10 g NiBr 2 H2O) g NiBr 2 H 2 O 1 mol NiBr 2 H 2 O = 7.572x10 5 = 7.57x10 5 mol of ions 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-2

3 c) Each mole of FeCl forms 1mole of Fe ions and moles of Cl ions, or a total of 4 moles of ions: FeCl(s) Fe (aq) Cl (aq). Recall that a mole contains 6.022x10 2 entities, so a mole of FeCl contains 6.022x10 2 units of FeCl, more easily expressed as formula units mol FeCl 4 mol ions Moles of ions = ( 2.2x10 FU FeCl ) x10 FU FeCl 1 mol FeCl = = mol of ions 4.1 Plan: To determine the total moles of ions released, write an equation that shows the compound dissociating into ions with the correct molar ratios. Convert mass and formula units to moles of compound and use the molar ratio to convert moles of compound to moles of ions. a) Each mole of Na2HPO 4 forms 2 moles of Na 2 ions and 1 mole of HPO 4 ions, or a total of moles of ions: Na2HPO 4 (s) 2Na 2 (aq) HPO 4 (aq). mol ions Moles of ions = ( 0.74 mol Na2HPO4) = = 2.20 mol of ions 1 mol Na2HPO4 b) Each mole of CuSO 4 5H 2 O forms 1 mole of Cu 2 2 ions and 1 mole of SO 4 ions, or a total of 2 moles of ions: CuSO4 5H 2 O(s) Cu 2 2 (aq) SO 4 (aq). The waters of hydration become part of the larger bulk of water. Convert mass to moles using the molar mass. Moles of ions = 4 2 (.86 g CuSO 5H O ) mol CuSO 5H O 2 mol ions g CuSO 5H O 1 mol CuSO 5H O =.0907x10 2 =.09x10 2 mol of ions c) Each mole of NiCl2 forms 1 mole of Ni 2 ions and 2 moles of Cl ions, or a total of moles of ions: NiCl2(s) Ni 2 (aq) 2Cl (aq). Recall that a mole contains 6.022x10 2 entities, so a mole of NiCl 2 contains 6.022x10 2 units of NiCl 2, more easily expressed as formula units mol NiCl2 mol ions Moles of ions = ( 8.66x10 FU NiCl2 ) x10 FU NiCl 2 1 mol NiCl2 = x10 = 4.1x10 mol of ions 4.14 Plan: To determine the total moles of ions released, write an equation that shows the compound dissociating into ions with the correct molar ratios. Convert the information given to moles of compound and use the molar ratio to convert moles of compound to moles of ions. Avogadro s number is used to convert moles of ions to numbers of ions. a) Each mole of AlCl forms 1mole of Al ions and moles of Cl ions: AlCl (s) Al (aq) Cl (aq). Molarity and volume must be converted to moles of AlCl. 10 L 0.45 mol AlCl Moles of AlCl ( 10. ml) = 1 ml L = mol AlCl Moles of Al Number of Al Moles of Cl 1 mol Al = = = mol Al 1 mol AlCl ( mol AlCl ) Number of Cl x10 Al ions = =.52287x 10 1 mol Al 22 =.5x10 22 Al ions ( mol Al ) mol Cl = ( mol AlCl ) = = 0.18 mol Cl 1 mol AlCl ions = ( mol Cl ) x10 Cl 1 mol Cl = x10 2 = 1.1x10 2 Cl ions 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-

4 b) Each mole of Li 2 SO 4 forms 2 moles of Li ions and 1 mole of SO 2 4 ions: Li 2 SO 4 (s) 2Li 2 (aq) SO 4 (aq). 10 L 2.59 g Li2SO4 1 mol Li2SO4 Moles of Li2SO 4 = ( 9.80 ml) = 2.085x10 1 ml 4 mol Li 2 SO 4 1 L g Li2SO4 Moles of Li ( 4 2 mol Li = 2.085x10 mol Li2SO4) = x10 1 mol Li2SO 4 = 4.62x10 4 mol Li x 10 Li Number of Li ions = ( x10 mol Li ) = x10 1 mol Li 20 = 2.78x10 20 Li ions 2 Moles of SO mol SO 4 = ( 2.085x10 mol Li2SO4) = 2.085x10 1 mol Li2SO 4 = 2.1x mol SO x 10 SO 4 Number of SO 4 ions = ( 2.085x10 mol SO4 ) 2 1 mol SO 4 = x10 20 = 1.9x SO 4 ions c) Each mole of KBr forms 1 mole of K ions and 1 mole of Br ions: KBr(s) K (aq) Br (aq) L.68 x10 FU KBr 1 mol KBr Moles of KBr = ( 245 ml) 2 = mol KBr 1 ml L 6.022x10 FU KBr Moles of K 1 mol K = ( mol KBr) = = 1.50x10 1 mol KBr 2 mol K x10 K Number of K ions = ( mol K ) = 9.016x10 1 mol K 21 = 9.02x10 21 K ions 1 mol Br Moles of Br = ( mol KBr) = = 1.50x10 1 mol KBr 2 mol Br x10 Br Number of Br ions = ( mol Br ) = 9.016x10 1 mol Br 21 = 9.02x10 21 Br ions 4.15 Plan: To determine the total moles of ions released, write an equation that shows the compound dissociating into ions with the correct molar ratios. Convert the information given to moles of compound and use the molar ratio to convert moles of compound to moles of ions. Avogadro s number is used to convert moles of ions to numbers of ions. a) Each mole of MgCl 2 forms 1 mole of Mg 2 ions and 2 moles of Cl ions: MgCl 2 (s) Mg 2 (aq) 2Cl (aq). 10 L 1.75 mol MgCl Moles of MgCl2 ( 88.mL) 2 = 1 ml L = mol MgCl 2 2 Moles of Mg 2 1 mol Mg 2 = ( mol MgCl2 ) = = 0.15 mol Mg 1 mol MgCl x10 Mg Number of Mg ions = ( mol Mg ) 2 = x10 1 mol Mg 22 = 9.x10 22 Mg 2 ions 2 mol Cl Moles of Cl = ( mol MgCl2 ) = 0.08 = 0.1 mol Cl 1 mol MgCl by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-4

5 x10 Cl ions = = x10 1 mol Cl 2 = 1.9x10 2 Cl ions b) Each mole of Al2(SO 4 ) forms 2 moles of Al 2 ions and moles of SO 4 ions: Al2(SO 4 ) (s) 2Al 2 (aq) SO 4 (aq). 10 L 0.22 g Al 2(SO 4) 1 mol Al 2(SO 4) Moles of Al2(SO 4 ) = ( 21 ml) 1 ml 1 L g Al 2(SO 4) = x10 4 mol Al 2 (SO 4 ) Number of Cl ( 0.08 mol Cl ) Moles of Al Number of Al Moles of SO 2 mol Al 4 ( x10 mol Al 2(SO 4) ) = = x10 1 mol Al 2(SO 4) 4 = 4.1x10 4 mol Al x10 Al ions = = x10 1 mol Al 20 = 2.5x10 20 Al ions 4 ( x10 mol Al ) 2 4 mol SO 4 = = x10 1 mol Al 2(SO 4) 4 = 6.2x10 4 mol SO ( x10 mol Al 2(SO 4) ) x10 SO 4 Number of SO mol SO 4 =.7286x10 20 =.7x SO 4 ions c) Each mole of CsNO forms 1 mole of Cs ions and 1 mole of NO ions: CsNO (s) Cs (aq) NO (aq) 21 Moles of CsNO = 8.8x10 FU CsNO 1 mol CsNO ( 1.65 L) 2 L 6.022x10 FU CsNO = mol CsNO Moles of Cs 4 2 ions = ( x10 mol SO ) 1 mol Cs = = = mol Cs 1 mol CsNO ( mol CsNO ) x10 Cs ions = = x10 1 mol Cs 22 = 1.46x10 22 Cs ions Number of Cs ( mol Cs ) Moles of NO 1 mol NO = = = mol NO 1 mol CsNO ( mol CsNO ) Number of NO ions = ( mol NO ) x10 NO 1 mol NO = x10 22 = 1.46x10 22 NO ions 4.16 Plan: The acids in this problem are all strong acids, so you can assume that all acid molecules dissociate completely to yield H ions and associated anions. One mole of HClO 4, HNO, and HCl each produce one mole of H upon dissociation, so moles H = moles acid. Calculate the moles of acid by multiplying the molarity (moles/l) by the volume in liters. a) HClO4(aq) H (aq) ClO 4 (aq) Moles H 0.25 mol = mol HClO 4 = ( 1.40 L) = 0.5 mol H 1L b) HNO(aq) H (aq) NO (aq) Moles H 10 L 0.92 mol = mol HNO = ( 6.8 ml) 1 ml 1 L = 6.256x10 = 6.x10 mol H c) HCl(aq) H (aq) Cl (aq) mol Moles H = mol HCl = ( 2.6 L) 1 L = = 0.22 mol H by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-5

6 4.17 Plan: The acids in this problem are all strong acids, so you can assume that all acid molecules dissociate completely to yield H ions and associated anions. One mole of HBr, HI, and HNO each produce one mole of H upon dissociation, so moles H = moles acid. Calculate the moles of acid by multiplying the molarity (moles/l) by the volume in liters. a) HBr(aq) H (aq) Br (aq) 10 L 0.75 mol Moles H = mol HBr = ( 1.4 ml) 1 ml 1 L = 1.05x10 = 1.0x10 mol H b) HI(aq) H (aq) I (aq) 10 L 1.98 mol Moles H = mol HI = ( 2.47 ml) 1 ml 1 L = x10 = 4.89x10 mol H c) HNO(aq) H (aq) NO (aq) Moles H 10 L mol = mol HNO = ( 95 ml) 1 ml 1 L = = mol H 4.18 Plan: Convert the mass of the seawater in kg to g and use the density to convert the mass of the seawater to volume in L. Convert mass of each compound to moles of compound and then use the molar ratio in the dissociation of the compound to find the moles of each ion. The molarity of each ion is the moles of ion divided by the volume of the seawater. To find the total molarity of the alkali metal ions [Group 1A(1)], add the moles of the alkali metal ions and divide by the volume of the seawater. Perform the same calculation to find the total molarity of the alkaline earth metal ions [Group 2A(2)] and the anions (the negatively charged ions). a) The volume of the seawater is needed. 10 g cm 1 ml 10 L Volume (L) of seawater = ( 1.00 kg) = L 1 kg g 1 cm 1 ml The moles of each ion are needed. If an ion comes from more than one source, the total moles are needed. NaCl: Each mole of NaCl forms 1 mole of Na ions and 1 mole of Cl ions: NaCl(s) Na (aq) Cl (aq) 1 mol NaCl Moles of NaCl = ( 26.5 g NaCl) = mol NaCl g NaCl Moles of Na 1 mol Na = ( mol NaCl) = mol Na 1 mol NaCl 1 mol Cl Moles of Cl = ( mol NaCl) = mol Cl 1 mol NaCl MgCl2: Each mole of MgCl2 forms 1 mole of Mg 2 ions and 2 moles of Cl ions: MgCl 2 (s) Mg 2 (aq) 2Cl (aq) 1 mol MgCl2 Moles of MgCl2 = ( 2.40 g MgCl2 ) = mol MgCl g MgCl mol Mg 2 Moles of Mg = ( mol MgCl2 ) = mol Mg 1 mol MgCl 2 2 mol Cl Moles of Cl = ( mol MgCl2 ) = mol Cl 1 mol MgCl 2 MgSO4: Each mole of MgSO4 forms 1 mole of Mg 2 ions and 1 mole of SO 2 4 ions: MgSO 4 (s) Mg 2 (aq) SO 2 4 (aq) 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-6

7 1 mol MgSO =.5 g MgSO4 = mol MgSO g MgSO4 Moles of MgSO 4 ( ) 4 Moles of Mg 2 1 mol Mg = 4 = mol Mg 1 mol MgSO 4 2 ( mol MgSO ) 2 Moles of SO4 2 1 mol SO 4 2 = ( mol MgSO4 ) = mol SO 1 mol MgSO 4 4 CaCl2: Each mole of CaCl2 forms 1 mole of Ca 2 ions and 2 moles of Cl ions: CaCl 2 (s) Ca 2 (aq) 2Cl (aq) Moles of CaCl Moles of Ca 2 1 mol CaCl2 1 mol Ca = 2 = mol CaCl g CaCl2 1 mol CaCl 2 2 ( 1.20 g CaCl ) 2 1 mol Ca = 2 = mol Ca 1 mol CaCl 2 2 ( mol CaCl ) 2 mol Cl Moles of Cl = ( mol CaCl2 ) = mol Cl 1 mol CaCl 2 KCl: Each mole of KCl forms 1 mole of K ions and 1 mole of Cl ions: KCl(s) K (aq) Cl (aq) Moles of KCl = ( 1.05 g KCl) Moles of K ( mol KCl) 1 mol KCl = mol KCl g KCl 1 mol K = = mol K 1 mol KCl 1 mol Cl Moles of Cl = ( mol KCl) = mol Cl 1 mol KCl NaHCO: Each mole of NaHCO forms 1 mole of Na ions and 1 mole of HCO ions: NaHCO (s) Na (aq) HCO (aq) 1 mol NaHCO Moles of NaHCO = ( 0.15 g NaHCO ) = mol NaHCO g NaHCO 1 mol Na = = mol Na 1 mol NaHCO Moles of Na ( mol NaHCO ) Moles of HCO 1 mol HCO = ( mol NaHCO ) = mol HCO 1 mol NaHCO NaBr Each mole of NaBr forms 1 mole of Na ions and 1 mole of Br ions: NaBr(s) Na (aq) Br (aq) Moles of NaBr = ( g NaBr) Moles of Na ( mol NaBr) Moles of Br 1 mol NaBr = mol NaBr g NaBr 1 mol Na = = mol Na 1 mol NaBr 1 mol Br = = mol Br 1 mol NaBr ( mol NaBr) by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-7

8 Total moles of each ion: Cl : = mol Cl Na : = mol Na Mg 2 2 : = mol Mg SO4 2 2 : mol SO 4 Ca 2 2 : mol Ca K : mol K HCO : mol HCO Br : mol Br Dividing each of the numbers of moles by the volume ( L) and rounding to the proper number of significant figures gives the molarities. M = mol L M Cl mol Cl = = = 0.55 M Cl L mol Na M Na = = = M Na L mol Mg 2 M Mg = = = M Mg L 2 M SO mol SO 4 2 = = = M SO L mol Ca 2 M Ca = = = M Ca L mol K M K = = = M K L M HCO mol HCO = = = M HCO L mol Br M Br = = = M Br L b) The alkali metal cations are Na and K. Add the molarities of the individual ions M Na M K = = M total for alkali metal cations c) The alkaline earth metal cations are Mg 2 and Ca 2. Add the molarities of the individual ions M Mg M Ca 2 = = M total for alkaline earth cations d) The anions are Cl, SO 2 4, HCO, and Br. Add the molarities of the individual ions M Cl M SO M HCO M Br = = M total for anions 4.19 Plan: Use the molarity and volume of the ions to find the moles of each ion. Multiply the moles of each ion by that ion s charge to find the total moles of charge. Since sodium ions have a 1 charge, the total moles of charge equals the moles of sodium ions mol Ca 2 Moles of Ca = ( 1.0 x10 L) = 15 mol Ca L mol charge 2 Moles of charge from Ca = ( 15 mol Ca ) 2 = 0. mol charge from Ca 1 mol Ca mol Fe Moles of Fe = ( 1.0x10 L) = 1.0 mol Fe L 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-8

9 mol charge = =.0 mol charge from Fe 1 mol Fe Total moles of charge = 0. mol.0 mol = mol charge Moles Na 1 mol Na = ( mol charge) = mol Na 1 mol charge Moles of charge from Fe ( 1.0 mol Fe ) 4.20 Plan: Write the total ionic and net ionic equations for the reaction given. The total ionic equation shows all soluble ionic substances dissociated into ions. The net ionic equation eliminates the spectator ions. New equations may be written by replacing the spectator ions in the given equation by other spectator ions. The reaction given has the following total ionic and net ionic equations: Total ionic equation: Ba 2 (aq) 2NO (aq) 2Na (aq) CO 2 (aq) BaCO (s) 2Na (aq) 2NO (aq) The spectator ions are underlined and are omitted: Net ionic equation: Ba 2 (aq) CO 2 (aq) BaCO (s) New equations will contain a soluble barium compound and a soluble carbonate compound. The new equations are: Molecular: BaCl 2 (aq) K 2 CO (aq) BaCO (s) 2KCl(aq) Total ionic: Ba 2 (aq) 2Cl (aq) 2K (aq) CO 2 (aq) BaCO (s) 2K (aq) 2Cl (aq) Molecular: BaBr2(aq) (NH 4 ) 2 CO (aq) BaCO (s) 2NH 4 Br(aq) Total ionic: Ba 2 (aq) 2Br (aq) 2NH 4 (aq) CO 2 (aq) BaCO (s) 2NH 4 (aq) 2Br (aq) 4.21 If the electrostatic attraction between the ions is greater than the attraction of the ions for water molecules, the ions will form a precipitate. This is the basis for the solubility rules Plan: Write the new cation-anion combinations as the products of the reaction and use the solubility rules to determine if any of the new combinations are insoluble. The spectator ions are the ions that are present in the soluble ionic compound. a) Ca(NO) 2 (aq) 2NaCl(aq) CaCl 2 (aq) 2NaNO (aq) Since the possible products (CaCl2 and NaNO ) are both soluble, no reaction would take place. b) 2KCl(aq) Pb(NO) 2 (aq) 2KNO (aq) PbCl 2 (s) According to the solubility rules, KNO is soluble but PbCl 2 is insoluble so a precipitation reaction takes place. The K and NO would be spectator ions, because their salt is soluble. 4.2 Plan: Use the solubility rules to predict the products of this reaction. Ions not involved in the precipitate are spectator ions and are not included in the net ionic equation. Assuming that the left beaker is AgNO (because it has gray Ag ions) and the right must be NaCl, then the NO is blue, the Na is brown, and the Cl is green. (Cl must be green since it is present with Ag in the precipitate in the beaker on the right.) Molecular equation: AgNO (aq) NaCl(aq) AgCl(s) NaNO (aq) Total ionic equation: Ag (aq) NO (aq) Na (aq) Cl (aq) AgCl(s) Na (aq) NO (aq) Net ionic equation: Ag (aq) Cl (aq) AgCl(s) 4.24 Plan: Write the new cation-anion combinations as the products of the reaction and use the solubility rules to determine if any of the new combinations are insoluble. The total ionic equation shows all soluble ionic substances dissociated into ions. The spectator ions are the ions that are present in the soluble ionic compound. The spectator ions are omitted from the net ionic equation. a) Molecular: Hg2(NO ) 2 (aq) 2KI(aq) Hg 2 I 2 (s) 2KNO (aq) Total ionic: Hg2 2 (aq) 2NO (aq) 2K (aq) 2I (aq) Hg 2 I 2 (s) 2K (aq) 2NO (aq) Net ionic: Hg2 2 (aq) 2I (aq) Hg 2 I 2 (s) Spectator ions are K and NO. 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-9

10 b) Molecular: FeSO 4 (aq) Sr(OH) 2 (aq) Fe(OH) 2 (s) SrSO 4 (s) Total ionic: Fe 2 (aq) SO 2 4 (aq) Sr 2 (aq) 2OH (aq) Fe(OH) 2 (s) SrSO 4 (s) Net ionic: This is the same as the total ionic equation because there are no spectator ions Plan: Write the new cation-anion combinations as the products of the reaction and use the solubility rules to determine if any of the new combinations are insoluble. The total ionic equation shows all soluble ionic substances dissociated into ions. The spectator ions are the ions that are present in the soluble ionic compound. The spectator ions are omitted from the net ionic equation. a) Molecular: CaCl2(aq) 2Cs PO 4 (aq) Ca (PO 4 ) 2 (s) 6CsCl(aq) Total ionic: Ca 2 (aq) 6Cl (aq) 6Cs (aq) 2PO 4 (aq) Ca (PO 4 ) 2 (s) 6Cs (aq) 6Cl (aq) Net ionic: Ca 2 (aq) 2PO 4 (aq) Ca (PO 4 ) 2 (s) Spectator ions are Cs and Cl. b) Molecular: Na2S(aq) ZnSO 4 (aq) ZnS(s) Na 2 SO 4 (aq) Total ionic: 2Na (aq) S 2 (aq) Zn 2 (aq) SO 2 4 (aq) ZnS(s) 2Na 2 (aq) SO 4 (aq) Net ionic: Zn 2 (aq) S 2 (aq) ZnS(s) Spectator ions are Na and SO Plan: A precipitate forms if reactant ions can form combinations that are insoluble, as determined by the solubility rules in Table 4.1. Create cation-anion combinations other than the original reactants and determine if they are insoluble. Any ions not involved in a precipitate are spectator ions and are omitted from the net ionic equation. a) NaNO(aq) CuSO 4 (aq) Na 2 SO 4 (aq) Cu(NO ) 2 (aq) No precipitate will form. The ions Na and SO 2 4 will not form an insoluble salt according to the first solubility rule which states that all common compounds of Group 1A ions are soluble. The ions Cu 2 and NO will not form an insoluble salt according to the solubility rule #2: All common nitrates are soluble. There is no reaction. b) A precipitate will form because silver ions, Ag, and bromide ions, Br, will combine to form a solid salt, silver bromide, AgBr. The ammonium and nitrate ions do not form a precipitate. Molecular: NH4Br(aq) AgNO (aq) AgBr(s) NH 4 NO (aq) Total ionic: NH4 (aq) Br (aq) Ag (aq) NO (aq) AgBr(s) NH 4 (aq) NO (aq) Net ionic: Ag (aq) Br (aq) AgBr(s) 4.27 Plan: A precipitate forms if reactant ions can form combinations that are insoluble, as determined by the solubility rules in Table 4.1. Create cation-anion combinations other than the original reactants and determine if they are insoluble. Any ions not involved in a precipitate are spectator ions and are omitted from the net ionic equation. a) Barium carbonate (BaCO) precipitates since the solubility rules state that all common carbonates are insoluble. Molecular: K2CO (aq) Ba(OH) 2 (aq) BaCO (s) 2KOH(aq) Total ionic: 2K (aq) CO 2 (aq) Ba 2 (aq) 2OH (aq) BaCO (s) 2K (aq) 2OH (aq) Net ionic: Ba 2 (aq) CO 2 (aq) BaCO (s) b) Aluminum phosphate (AlPO4) precipitates since most common phosphates are insoluble; the sodium nitrate is soluble. Molecular: Al(NO) (aq) Na PO 4 (aq) AlPO 4 (s) NaNO (aq) Total ionic: Al (aq) NO (aq) Na (aq) PO 4 (aq) AlPO 4 (s) Na (aq) NO (aq) Net ionic: Al (aq) PO 4 (aq) AlPO 4 (s) 4.28 Plan: Write a balanced equation for the chemical reaction described in the problem. By applying the solubility rules to the two possible products (NaNO and PbI 2 ), determine that PbI 2 is the precipitate. By using molar relationships, determine how many moles of Pb(NO ) 2 are required to produce g of PbI 2. The molarity is calculated by dividing moles of Pb(NO) 2 by its volume in liters. The reaction is: Pb(NO) 2 (aq) 2NaI(aq) PbI 2 (s) 2NaNO (aq). 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-10

11 1 mol PbI 1 mol Pb(NO ) = g PbI2 = mol Pb(NO ) g PbI 1 mol PbI 2 2 Moles of Pb(NO ) 2 ( ) 2 2 Moles of Pb 2 = moles of Pb(NO ) 2 = mol Pb 2 2 Molarity of Pb 2 moles Pb mol 1 ml = = 2 volume of Pb 8.5 ml = = M Pb 2 10 L 4.29 Plan: Write a balanced equation for the chemical reaction described in the problem. By applying the solubility rules to the two possible products (KNO and AgCl), determine that AgCl is the precipitate. By using molar relationships, determine how many moles of AgNO are required to produce g of AgCl. The molarity is calculated by dividing moles of AgNO by its volume in liters. The reaction is AgNO(aq) KCl(aq) AgCl(s) KNO (aq). 1 mol AgCl 1 mol AgNO Moles of AgNO = ( g AgCl) = mol AgNO 14.4 g AgCl 1 mol AgCl Moles of Ag = moles of AgNO = mol Ag Molarity of Ag moles Ag mol 1 ml = = volume of Ag 25.0 ml = = 0.25 M Ag 10 L 4.0 Plan: A precipitate forms if reactant ions can form combinations that are insoluble, as determined by the solubility rules in Table 4.1. Create cation-anion combinations other than the original reactants and determine if they are insoluble. Any ions not involved in a precipitate are spectator ions and are omitted from the net ionic equation. Use the molar ratio in the balanced net ionic equation to calculate the mass of product. a) The yellow spheres cannot be ClO4 or NO as these ions form only soluble compounds. So the yellow sphere must be SO 2 4. The only sulfate compounds possible that would be insoluble are Ag 2 SO 4 and PbSO 4. The precipitate has a 1:1 ratio between its ions. Ag 2 SO 4 has a 2:1 ratio between its ions. Therefore the blue spheres are Pb 2 and the yellow spheres are SO 2 4. The precipitate is thus PbSO 4. b) The net ionic equation is Pb 2 (aq) SO 2 4 (aq) PbSO 4 (s) x10 mol Pb 1 mol PbSO4 0. g PbSO4 c) Mass (g) of PbSO4 = ( 10 Pb spheres) Pb sphere 1 mol Pb 1 mol PbSO4 = = 1.5 g PbSO Plan: A precipitate forms if reactant ions can form combinations that are insoluble, as determined by the solubility rules in Table 4.1. Create cation-anion combinations other than the original reactants and determine if they are insoluble. Any ions not involved in a precipitate are spectator ions and are omitted from the net ionic equation. Use the molar ratio in the balanced net ionic equation to calculate the mass of product. a) There are 9 purple spheres representing cations and 7 green spheres representing anions. In the precipitate, there are 8 purple spheres (cations) and 4 green spheres (anions), indicating a 2:1 ratio between cation and anion in the compound. Only Reaction produces a precipitate (Ag2SO 4 ) fitting this description: Li2SO 4 (aq) 2AgNO (aq) 2LiNO (aq) Ag 2 SO 4 (s) Reaction 1 does not produce a precipitate since all common nitrate and chloride compounds are soluble. Reaction 2 does not produce a precipitate since all common perchlorate and chloride compounds are soluble. Reaction 4 produces a precipitate, PbBr2, but it has a cation:anion ratio of 1:2, instead of 2:1. Total ionic equation for Reaction = 2Li (aq) SO 2 4 (aq) 2Ag (aq) 2NO (aq) 2Li (aq) 2NO (aq) Ag 2 SO 4 (s) Net ionic equation = 2Ag (aq) SO 2 4 (aq) Ag 2 SO 4 (s) b) There are 4 unreacted spheres of ions. Number of ions = ( 4 spheres) 2 2.5x10 mol ions 6.022x10 ions = 6.022x10 1 sphere 1 mol ions 21 = 6.0x10 21 ions by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-11

12 c) Mass (g) of solid = x10 mol SO 4 ions 1 mol Ag2SO g Ag2SO4 ( 4 spheres of SO 4 ions) 2 1 sphere 1 mol SO 4 1 mol Ag2SO4 =.119 =.1 g solid 4.2 Plan: Write a balanced equation for the reaction. Find the moles of AgNO by multiplying the molarity and volume of the AgNO solution; use the molar ratio in the balanced equation to find the moles of Cl present in the ml sample. Then, convert moles of Cl into grams, and convert the sample volume into grams using the given density. The mass percent of Cl is found by dividing the mass of Cl by the mass of the sample volume and multiplying by 100. The balanced equation is AgNO(aq) Cl (aq) AgCl(s) NO (aq). 10 L mol AgNO Moles of AgNO ( 5.6 ml) = 1 ml L = mol AgNO 1 mol Cl 5.45 g Cl Mass (g) of Cl = ( mol AgNO ) = g Cl 1 mol AgNO 1 mol Cl Mass (g) of seawater sample = ( ml) g ml = g sample Mass % Cl mass Cl = x 100% = g Cl x 100% = = 2.206% Cl mass sample g sample 4. Plan: Write the reaction between aluminum sulfate and sodium hydroxide and check the solubility rules to determine the precipitate. Spectator ions are omitted from the net ionic equation. Find the moles of sodium hydroxide by multiplying its molarity by its volume in liters; find the moles of aluminum sulfate by converting grams per liter to moles per liter and multiplying by the volume of that solution. To determine which reactant is limiting, calculate the amount of precipitate formed from each reactant, assuming an excess of the other reactant, using the molar ratio from the balanced equation. The smaller amount of precipitate is the answer. a) According to the solubility rules, most common sulfate compounds are soluble, but most common hydroxides are insoluble. Aluminum hydroxide is the precipitate. Total ionic equation: Al 2 (SO 4 ) (aq) 6NaOH(aq) Na 2 SO 4 (aq) 2Al(OH) (s) Net ionic equation: Al (aq) OH (aq) Al(OH) (s) 10 L 15.8 g Al 2(SO 4) 1 mol Al 2(SO 4) b) Moles of Al2(SO 4 ) = ( 627 ml) 1 ml L g Al 2(SO 4) = mol Al 2 (SO 4 ) 2 mol Al(OH) g Al(OH) Mass (g) of Al(OH) from Al 2 (SO 4 ) = ( mol Al 2(SO 4) ) 1 mol Al 2(SO 4) 1 mol Al(OH) = g Al(OH) 10 L 0.5 mol NaOH Moles of NaOH = ( ml) 1 ml L = mol NaOH 2 mol Al(OH) g Al(OH) Mass (g) of Al(OH) from NaOH = ( mol NaOH) 6 mol NaOH 1 mol Al(OH) = = 2.57 g Al(OH) NaOH is the limiting reagent. 4.4 Plan: Write the chemical reaction between the two reactants. Then write the total ionic equation in which all soluble ionic substances are dissociated into ions. Omit spectator ions in the net ionic equation. 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-12

13 The molecular equation is H2SO 4 (aq) Sr(OH) 2 (aq) SrSO 4 (s) 2H 2 O(l) The total ionic equation is: 2H (aq) SO 2 4 (aq) Sr 2 (aq) 2OH (aq) SrSO 4 (s) 2H 2 O(l) According to the solubility rules, SrSO4 is insoluble and therefore does not dissociate into ions. Since there are no spectator ions, the total and net ionic equations are the same. 4.5 Plan: Review the section on acid-base reactions. a) Any three of HCl, HBr, HI, HNO, H 2 SO 4, or HClO 4 b) Any three of NaOH, KOH, Ca(OH) 2, Sr(OH) 2, Ba(OH) 2 c) Strong acids and bases dissociate 100% into ions in aqueous solution. 4.6 Plan: Review the section on acid-base reactions. a) There are many possibilities including: acetic acid (HC2H O 2 ), chlorous acid (HClO 2 ), and nitrous acid (HNO 2 ). All acids are weak except for the six strong acids listed in the text. b) NH c) Strong acids and bases dissociate 100% into ions and are therefore strong electrolytes; weak acids and bases dissociate much less than this (typically less than 10%) in aqueous solution and are therefore weak electrolytes. The electrical conductivity of a solution of a strong acid or base would be much higher than that of a weak acid or base of equal concentration. 4.7 Plan: Since strong acids and bases dissociate completely in water, these substances can be written as ions in a total ionic equation; since weak acids and bases dissociate into ions only to a small extent, these substances appear undissociated in total ionic equations. a) Acetic acid is a weak acid and sodium hydroxide is a strong base: Molecular equation: CH COOH(aq) NaOH(aq) CH COONa(aq) H 2 O(l) Total ionic equation: CHCOOH (aq) Na (aq) OH (aq) Na (aq) CH COO (aq) H 2 O(l) Net ionic equation (remove the spectator ion Na ): CH COOH(aq) OH (aq) CH COO (aq) H 2 O(l) Hydrochloric acid is a strong acid: Molecular equation: HCl(aq) NaOH(aq) NaCl(aq) H 2 O(l) Total ionic equation: H (aq) Cl (aq) Na (aq) OH (aq) Na (aq) Cl (aq) H 2 O(l) Net ionic equation (remove the spectator ions Na and Cl ): H (aq) OH (aq) H 2 O(l) The difference in the net ionic equation is due to the fact that CHCOOH is a weak acid and dissociates very little while HCl is a strong acid and dissociates completely. b) When acetic acid dissociates in water, most of the species in the solution is un-ionized acid, CH COOH(aq); the amounts of its ions, H and CH COO, are equal but very small: [CH COOH] >> [H ] = [CH COO ]. 4.8 Plan: Remember that strong acids and bases can be written as ions in the total ionic equation but weak acids and bases cannot be written as ions. Omit spectator ions from the net ionic equation. a) KOH is a strong base and HBr is a strong acid; both may be written in dissociated form. KBr is a soluble compound since all Group 1A(1) compounds are soluble. Molecular equation: KOH(aq) HBr(aq) KBr(aq) H 2 O(l) Total ionic equation: K (aq) OH (aq) H (aq) Br (aq) K (aq) Br (aq) H 2 O(l) Net ionic equation: OH (aq) H (aq) H 2 O(l) The spectator ions are K (aq) and Br (aq). b) NH is a weak base and is written in the molecular form. HCl is a strong acid and is written in the dissociated form (as ions). NH4Cl is a soluble compound, because all ammonium compounds are soluble. Molecular equation: NH(aq) HCl(aq) NH 4 Cl(aq) Total ionic equation: NH(aq) H (aq) Cl (aq) NH 4 (aq) Cl (aq) Net ionic equation: NH(aq) H (aq) NH 4 (aq) Cl is the only spectator ion. 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-1

14 4.9 Plan: Remember that strong acids and bases can be written as ions in the total ionic equation but weak acids and bases cannot be written as ions. Omit spectator ions from the net ionic equation. a) CsOH is a strong base and HNO is a strong acid; both may be written in dissociated form. CsNO is a soluble compound since all nitrate compounds are soluble. Molecular equation: CsOH(aq) HNO (aq) CsNO (aq) H 2 O(l) Total ionic equation: Cs (aq) OH (aq) H (aq) NO (aq) Cs (aq) NO (aq) H 2 O(l) Net ionic equation: OH (aq) H (aq) H 2 O(l) Spectator ions are Cs and NO. b) HC2H O 2 is a weak acid and is written in the molecular form. Ca(OH) 2 is a strong base and is written in the dissociated form (as ions). Ca(C 2 H O 2 ) 2 is a soluble compound, because all acetate compounds are soluble. Molecular equation: Ca(OH) 2(aq) 2HC 2 H O 2 (aq) Ca(C 2 H O 2 ) 2 (aq) 2H 2 O(l) Total ionic equation: Ca 2 (aq) 2OH (aq) 2HC 2 H O 2 (aq) Ca 2 (aq) 2C 2 H O 2 (aq) 2H 2 O(l) Net ionic equation: OH (aq) HC 2 H O 2 (aq) C 2 H O 2 (aq) H 2 O(l) Spectator ion is Ca Plan: Write an acid-base reaction between CaCO and HCl. Remember that HCl is a strong acid. Calcium carbonate dissolves in HCl(aq) because the carbonate ion, a base, reacts with the acid to form H2CO which decomposes into CO 2 (g) and H 2 O(l). CaCO(s) 2HCl(aq) CaCl 2 (aq) H 2 CO (aq) Total ionic equation: CaCO (s) 2H (aq) 2Cl (aq) Ca 2 (aq) 2Cl (aq) H 2 O(l) CO 2 (g) Net ionic equation: CaCO (s) 2H (aq) Ca 2 (aq) H 2 O(l) CO 2 (g) 4.41 Plan: Write an acid-base reaction between Zn(OH) 2 and HNO. Remember that HNO is a strong acid. Zinc hydroxide dissolves in HCl(aq) because the hydroxide ion, a base, reacts with the acid to form soluble zinc nitrate and water. Zn(OH) 2 (s) 2HNO (aq) Zn(NO ) 2 (aq) 2H 2 O(aq) Total ionic equation: Zn(OH) 2 (s) 2H (aq) 2NO (aq) Zn 2 (aq) 2NO (aq) 2H 2 O(l) Net ionic equation: Zn(OH) 2 (s) 2H (aq) Zn 2 (aq) 2H 2 O(l) 4.42 Plan: Write a balanced equation. Find the moles of KOH from the molarity and volume information and use the molar ratio in the balanced equation to find the moles of acid present. Divide the moles of acid by its volume to determine the molarity. The reaction is: KOH(aq) CHCOOH(aq) CH COOK(aq) H 2 O(l) 10 L mol KOH Moles of KOH = ( ml) 1 ml L = mol KOH 1mol CHCOOH Moles of CH COOH = ( mol KOH) = mol CH COOH 1 mol KOH Molarity of CH COOH = mol CH COOH 1 ml ml 10 L = = M CH COOH 4.4 Plan: Write a balanced equation. Find the moles of NaOH from the molarity and volume information and use the molar ratio in the balanced equation to find the moles of acid present. Divide the moles of acid by its volume to determine the molarity. 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-14

15 The reaction is: 2NaOH(aq) H2SO 4 (aq) Na 2 SO 4 (aq) 2H 2 O(l) 10 L mol NaOH Moles of NaOH = ( ml) 1 ml L = mol NaOH 1mol H2SO4 Moles of H 2 SO 4 = ( mol NaOH) = mol H 2 SO4 2 mol NaOH Molarity of H2SO = mol H2SO4 1 ml ml 10 L = = M H SO Plan: Write a balanced equation. Find the moles of H 2 SO 4 from the molarity and volume information and use the molar ratio in the balanced equation to find the moles of NaHCO required to react with that amount of H 2 SO 4. Divide the moles of NaHCO by its molarity to find the volume. The reaction is: 2NaHCO(aq) H 2 SO 4 (aq) Na 2 SO 4 (aq) 2 H 2 O(l) 2CO 2 (g) 10 L 2.6 mol H2SO4 Moles of H2SO 4 = ( 88 ml) 1 ml L = mol H 2 SO4 2 mol NaHCO Moles of NaHCO = ( mol H2SO4) = mol NaHCO 1 mol H2SO4 1L 1mL Volume (ml) of NaHCO = ( mol NaHCO ) 1.6 mol NaHCO 10 L = 286 = 2.9 x 10 2 ml NaHCO 4.45 Plan: Balance the reaction. Convert the amount of UO 2 from kg to g to moles; use the molar ratio in the balanced reaction to find the moles of HF required to react with the moles of UO2. Divide moles of HF by its molarity to calculate the volume. The reaction is: UO2(s) 4HF(aq) UF 4 (s) 2H 2 O(l) 10 g 1 mol UO2 Moles of UO2 = ( 2.15 kg UO2 ) = mol UO2 1 kg g UO2 4 mol HF Moles of HF = ( mol UO2 ) = mol HF 1 mol UO2 1L Volume (L) of HF = ( mol HF) = = 1. L HF 2.40 mol HF 4.46 Plan: Write balanced equations for the reaction of NaOH with oxalic acid, benzoic acid, and HCl. Find the moles of added NaOH from the molarity and volume information; then use the molarity and volume information for HCl to find the moles of HCl required to react with the excess NaOH. Use the molar ratio in the NaOH/HCl reaction to find the moles of excess NaOH. The moles of NaOH required to titrate the acid samples is the difference of the added NaOH and the excess NaOH. Let x = mass of benzoic acid and x = mass of oxalic acid. Convert the mass of each acid to moles using the molar mass and use the molar ratios in the balanced reactions to find the amounts of each acid. Mass percent is calculated by dividing the mass of benzoic acid by the mass of the sample and multiplying by 100. Oxalic acid is H2C 2 O 4 and benzoic acid is HC 7 H 5 O 2. The reactions are: NaOH(aq) HCl(aq) NaCl(aq) H2O(l) 2NaOH(aq) H2C 2 O 4 (aq) Na 2 C 2 O 4 (aq) 2H 2 O(l) NaOH(aq) HC7H 5 O 2 (aq) NaC 7 H 5 O 2 (aq) H 2 O(l) 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-15

16 Moles of NaOH added = ( ml) 10 L mol NaOH 1 ml 1 L = mol NaOH 10 L mol HCl Moles of added HCl = ( ml) 1 ml 1 L = mol HCl 1 mol NaOH Moles of excess NaOH = ( mol HCl) 1 mol HCl = mol NaOH Moles of NaOH required to titrate sample = moles NaOH added moles excess NaOH = mol mol = mol NaOH Let x = mass of HC 7 H 5 O 2 and x = mass of H 2 C 2 O Moles of NaOH required to titrate HC7H 5 O 2 = 1 mol HC7H5O2 1 mol NaOH ( x g HC7H5O2) = x g HC7H5O2 1 mol HC7H5O2 1 mol H2C2O4 2 mol NaOH Moles of NaOH required to titrate H 2 C 2 O 4 = ((0.471 x) g H2C2O4) g H2C2O4 1 mol H2C2O4 = x Moles of NaOH required to titrate sample = mol = x ( x) = x = x = x = mass of HC 7 H 5 O Mass % of HC = mass of HC H O g mass of sample g = = 5.14% H 5 O 2 ( 100 ) = ( 100) 4.47 Plan: Write balanced reactions between HNO and each of the bases. Find the moles of HNO from its molarity and volume. Let x = mass of Al(OH) and x = mass of Mg(OH) 2. Convert the mass of each base to moles using the molar mass and use the molar ratios in the balanced reactions to find the amounts of each base. Mass percent is calculated by dividing the mass of Al(OH) by the mass of the sample and multiplying by 100. The reactions are: HNO(aq) Al(OH) (aq) Al(NO ) (aq) H 2 O(l) 2HNO(aq) Mg(OH) 2 (aq) Mg(NO ) 2 (aq) 2H 2 O(l) 10 L mol HNO Moles of HNO ( 17.0 ml) = 1 ml 1 L = mol HNO Let x = mass of Al(OH) and x = mass of Mg(OH) 2 Moles of HNO required to titrate Al(OH) = 1 mol Al(OH) mol HNO ( x g Al(OH) ) = x g Al(OH) 1 mol Al(OH) Moles of HNO required to titrate Mg(OH) 2 = 1 mol Mg(OH) 2 2 mol HNO (( x) g Mg(OH) 2 ) 58. g Mg(OH) 2 1 mol Mg(OH) 2 = x Moles of HNO required to titrate sample = mol = x ( x) = x g = x = mass of Al(OH) Mass % of Al(OH) = mass of Al(OH) g ( 100 ) = ( 100) mass of sample g = = 7.25% by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-16

17 4.48 Plan: Recall that oxidation is the loss of electrons and reduction is the gain of electrons. The electrons that a substance gains during reduction must come from somewhere. So there must be an oxidation in which electrons are lost, to provide the electrons gained during reduction Plan: An oxidizing agent gains electrons and therefore has an atom whose oxidation number decreases during the reaction. Use the Rules for Assigning an Oxidation Number to assign S in H 2 SO 4 an O.N. and see if this oxidation number changes during the reaction. An acid transfers a proton during reaction. a) In H2SO 4, hydrogen has an O.N. of 1, for a total of 2; oxygen has an O.N. of 2 for a total of 8. The S has an O.N. of 6. In SO 2, the O.N. of oxygen is 2 for a total of 4 and S has an O.N. of 4. So the S has been reduced from 6 to 4 and is an oxidizing agent. Iodine is oxidized during the reaction. b) The oxidation number of S is 6 in H2SO 4 ; in BaSO 4, Ba has an O.N. of 2, the four oxygen atoms have a total O.N. of 8, and S is again 6. Since the oxidation number of S (or any of the other atoms) did not change, this is not a redox reaction. H 2 SO 4 transfers a proton to F to produce HF, so it acts as an acid Plan: Consult the Rules for Assigning an Oxidation Number. The sum of the O.N. values for the atoms in a molecule equals zero, while the sum of the O.N. values for the atoms in an ion equals the ion s charge. a) NH2OH. Hydrogen has an O.N. of 1, for a total of for the three hydrogen atoms. Oxygen has an O.N. of 2. The O.N. of N must be 1 since [( 1) () ( 2)] = 0. N = 1 b) N2F 4. The O.N. of each fluorine is 1 for a total of 4; the sum of the O.N.s for the two N atoms must be 4, so each N has an O.N. of 2. N = 2 c) NH 4. The O.N. of each hydrogen is 1 for a total of 4; the O.N. of nitrogen must be since the overall sum of the O.N.s must be 1: [( ) (4)] = 1 N = d) HNO 2. The O.N. of hydrogen is 1 and that of each oxygen is 2 for a total of 4 from the oxygens. The O.N. of nitrogen must be since [(1) () ( 4)] = 0. N = 4.51 Plan: Consult the Rules for Assigning an Oxidation Number. The sum of the O.N. values for the atoms in a molecule equals zero. a) SOCl2. The O.N. of oxygen is 2 and that of each chlorine is 1 for a total of 2 for the two chlorine atoms. The O.N. of sulfur must be 4 since [(4) ( 2) ( 2)] = 0. S = 4 b) H2S 2. The O.N. of each hydrogen is 1, for a total of 2. The sum of the O.N.s of the two sulfur atoms must equal 2, so the O.N. of each S atom is 1. S = 1 c) H 2 SO. The O.N. of each hydrogen atom is 1 for a total of 2; the O.N. of each oxygen atom is 2 for a total of 6. The O.N. of the sulfur must be 4 since [(2) (4) ( 6)] = 0. S = 4 d) Na 2 S. The O.N. of each sodium [Group 1A(1)] is 1, for a total of 2. The O.N. of sulfur is 2. S = Plan: Consult the Rules for Assigning an Oxidation Number. The sum of the O.N. values for the atoms in a molecule equals zero, while the sum of the O.N. values for the atoms in an ion equals the ion s charge. a) AsH. H is combined with a nonmetal, so its O.N. is 1 (Rule ). Three H atoms have a sum of. To have a sum of 0 for the molecule, As has an O.N. of. As = b) H2AsO 4. The O.N. of H in this compound is 1, for a total of 2. The O.N. of each oxygen is 2, for a total of 8. As has an O.N. of 5 since [(2) (5) ( 8)] = 1, the charge of the ion. As = 5 c) AsCl. Each chlorine has an O.N. of 1, for a total of. The O.N. of As is. As = 4.5 Plan: Consult the Rules for Assigning an Oxidation Number. The sum of the O.N. values for the atoms in a molecule equals zero, while the sum of the O.N. values for the atoms in an ion equals the ion s charge. 2 a) H2P 2 O 7. The O.N.of each hydrogen is 1, for a total of 2; the O.N. of each oxygen is 2, for a total of 14. The sum of the O.N.s of the two phosphorus atoms must be 10 since [(2) (10) ( 14)] = 2, the charge of the ion. Each of the two phosphorus atoms has an O.N. of 5. P = 5 b) PH 4. The O.N. of each hydrogen is 1, for a total of 4. The O.N. of P is since [( ) (4)] = 1, the charge of the ion. P = 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-17

18 c) PCl 5. The O.N. of each Cl is 1, for a total of 5. The O.N. of P is therefore 5. P = Plan: Consult the Rules for Assigning an Oxidation Number. The sum of the O.N. values for the atoms in a molecule equals zero, while the sum of the O.N. values for the atoms in an ion equals the ion s charge. a) MnO4 2. The O.N. of each oxygen is 2, for a total of 8; the O.N. of Mn must be 6 since [(6) ( 8)] = 2, the charge of the ion. Mn = 6 b) Mn 2 O. The O.N. of each oxygen is 2, for a total of 6; the sum of the O.N.s of the two Mn atoms must be 6. The O.N. of each manganese is. Mn = c) KMnO 4. The O.N. of potassium is 1 and the O.N. of each oxygen is 2, for a total of 8. The O.N. of Mn is 7 since [(1) (7) ( 8)] = 0. Mn = Plan: Consult the Rules for Assigning an Oxidation Number. The sum of the O.N. values for the atoms in a molecule equals zero, while the sum of the O.N. values for the atoms in an ion equals the ion s charge. a) CrO. The O.N. of each oxygen atom is 2, for a total of 6. The O.N. of chromium must be 6. Cr = 6 2 b) Cr2O 7. The O.N. of each oxygen is 2, for a total of 14. The sum of the O.N.s of the two chromium atoms must be 12 since [(12) ( 14)] = 2, the charge of the ion. Each of the two chromium atoms has an O.N. of 6. Cr = 6 c) Cr2(SO 4 ). It is convenient to treat the polyatomic ion SO 2 4 as a unit with a 2 charge, for a total of 6 for the three sulfate ions. The sum of the two chromium atoms must be 6 and the O.N. of each chromium atom is. Cr = 4.56 Plan: First, assign oxidation numbers to all atoms following the rules. The reactant that is the reducing agent contains an atom that is oxidized (O.N. increases from the left side to the right side of the equation). The reactant that is the oxidizing agent contains an atom that is reduced (O.N. decreases from the left side to the right side of the equation). Recognize that the agent is the compound that contains the atom that is oxidized or reduced, not just the atom itself. a) H 2 C 2 O 4 (aq) 2MnO 4 (aq) 6H (aq) 2Mn 2 (aq) 10CO 2 (g) 8H 2 O(l) Mn in MnO4 changes from 7 to 2 (reduction). Therefore, MnO 4 is the oxidizing agent. C in H 2 C 2 O 4 changes from to 4 (oxidation), so H 2 C 2 O 4 is the reducing agent. b) Cu(s) 8H (aq) 2NO (aq) Cu 2 (aq) 2NO(g) 4H 2 O(l) Cu changes from 0 to 2 (is oxidized) and Cu is the reducing agent. N changes from 5 (in NO ) to 2 (in NO) and is reduced, so NO is the oxidizing agent Plan: First, assign oxidation numbers to all atoms following the rules. The reactant that is the reducing agent contains an atom that is oxidized (O.N. increases from the left side to the right side of the equation). The reactant that is the oxidizing agent contains an atom that is reduced (O.N. decreases from the left side to the right side of the equation). Recognize that the agent is the compound that contains the atom that is oxidized or reduced, not just the atom itself a) Sn(s) 2H (aq) Sn 2 (aq) H 2 (g) Sn changes from 0 to 2 (is oxidized) so Sn is the reducing agent. H changes from 1 to 0 (is reduced) so H is the oxidizing agent. b) H (aq) H 2 O 2 (aq) 2Fe 2 (aq) 2Fe (aq) 2H 2 O(l) Oxygen changes from 1 in H2O 2 to 2 in H 2 O (is reduced) so H 2 O 2 is the oxidizing agent. Fe changes from 2 to (is oxidized) so Fe 2 is the reducing agent. 201 by McGraw-Hill Education. This is proprietary material solely for authorized instructor use. Not authorized for sale or distribution in any 4-18